Tail control and transfer adhesives for rolled paper products

ABSTRACT

A novel adhesive composition for tail control of rolled paper stock, said composition including a modified starch, polyethylene resin and water. The adhesive is applied onto the paper stock so as to form a non-continuous film.

This invention relates to an improved adhesive composition for use inpaper converting, to the process of applying the improved adhesive torolled paper stock, and to the rolled paper products produced thereby.The adhesive composition of the present invention is a repulpable,easy-release adhesive which has a very high initial wet tack, and whichhas particular application to tail control of rolled paper products.

In the manufacture of rolled paper products, e.g., paper towels andtoilet tissue, parent rolls of paper of up to five feet in diameter andlarger are mounted on a piece of equipment called a rewinder or aslitter/rewinder. The parent rolls of paper may have widths of up to 100feet, and these rolls of paper are rewound through the rewinderapparatus onto cylindrical cores of the same width. Initially, thecylindrical cores are placed on a rotatable mandrel which is indexedthrough an adhesive application sequence or through a non-adhesivetransfer system such as a vacuum system. If an adhesive applicationsequence is employed, an adhesive known in the art as a transferadhesive is applied to the cylindrical core at predetermined spacings,usually by means of applicator rollers. Thereafter, theadhesive-carrying core is rotated at the same speed as the paper webbeing fed through the rewinder from the parent paper roll. Dependingupon the type of rewinder equipment, the web speed of the paper rangesup to about 3000 feet per minute. The sheet of paper advancing throughthe rewinder is then picked up by the rotating, adhesive-carrying coreso that the sheet is rewound upon the core. Rewinding continues until apre-selected length of paper or preselected roll diameter has beenrewound upon the core. At that time, the paper sheet is automaticallycut across the entire width, and the loose end of the paper web attachedto the parent roll is immediately transferred onto another rotating,adhesive-carrying cylindrical core.

The rewound roll is then slit at predetermined intervals in order toprovide final rolled paper products of desired width. For example, therewound paper roll may be slit into a plurality of rolls of paper towelsor rolls of toilet tissue, depending upon the grade of paper rewound.This slitting operation may be carried out either on or off the rewinderapparatus; but whether slitting is contemplated on or off the rewinder,some technique for tail conrol must be effected prior to the slitting.That is, the tail, which is the last sheet, or sheets, or wrap of theroll of paper wound onto the cylindrical core, must be secured to therewound paper roll in order to prevent the tail from being loose,unraveled, or unwound during subsequent operations. This invention isoperable to "tie" the loose paper tail, and the only purpose of such atail control operation is to prevent unraveling of the paper from therewound roll until the individual paper product rolls have beenpackaged. After packaging, there is no need for further tail control.Rather, it is desired that the "tie"bond self-release upon packaging.

Present tail control systems utilize either water, or tape, oradhesives. For very soft and light paper products, such as toilettissue, water has been used for bonding the paper tail to the completedroll. However, this is not very effective with high speed rewindingsystems. When adhesive tail control is utilized, the adhesive is appliedto the rewound paper roll in a preselected pattern by means of sprays,daubers, or spitters. Spitters apply the adhesive in globs, leaving ahighly unattractive finished product. Daubers apply the adhesive bymeans of wheels and also result in an unattractive final product. Whenused with most adhesives, spray systems (with or without air) also causea visible deposition of adhesive on the paper.

There are many characteristics which should be possessed by an idealtail control adhesive. The adhesive should have a very high initial tackfor rapid bonding of the tail or outer wrap to the rewound roll. Also,the adhesive should possess release properties such that, upon drying,the bond between the tail or outer wrap and the body of the roll willrelease, providing ease of roll unwind by the consumer. Moreover, it isimportant that the adhesive be repulpable; that is, it should be watersoluble or water dispersible so that the product can be reworked by themanufacturer if necessary. Additionally, the adhesive must be non-toxicso as not to be detrimental to the consumer. Finally, the adhesiveshould not stain the paper product and should leave little or no visibledeposition thereon, and should not impair the hand or softness of thesubstrate that has been bonded.

Adhesives presently used for tail control in paper converting do notembody all of the above-mentioned desirable characteristics. Forexample, hot melt adhesives which have been formulated for tail controlusually have good initial tack but frequently possess poor release orunwind properties, poor flexibility, and leave a visible stain on thepaper substrate. Moreover, most hot melt adhesives are not repulpable.Other tail control adhesives, which have been formulated for roomtemperature application, are usually repulpable and have easy-releaseproperties. However, such adhesives usually possess insufficient initialtack for efficient plant operation, especially in high speed rewindingsystems. Failure to rapidly and securely bond the tail to the rewoundroll often results in the necessity of shutting down the rewindingoperation. Finally, present-day paper towel and toilet paper rollproducts are characterized by tail control adhesives that leave visibleadhesive stains and/or leave a visible adhesive deposition on the paperand/or impair the hand and softness of the paper substrate that has beenbonded.

It is accordingly a principal object of the present invention to providean improved adhesive composition for use in tail control of rolled paperstock.

Another object of the present invention is to provide an improvedadhesive composition for tail control of rolled substrate material,which adhesive has a high initial tack, has easy-release properties, isrepulpable, is non-toxic, leaves no visible deposition or stain upon thesubstrate, and which does not impair the hand of the substrate.

It is a further object of the present invention to provide an improvedprocess for tail control of rolled paper stock.

It is an additional object of the present invention to provide animproved transfer adhesive composition for application to cylindricalcores for efficient substrate pickup in rewinding operations.

It is also an object of the present invention to provide an improvedprocess for applying the transfer adhesive to cylindrical cores.

Another object of the present invention is to provide improved rolledpaper products having the first-wound sheet bonded to a cylindrical coreand/or the last-wound sheet or outer wrap bonded to the roll by arepulpable, easy-release adhesive comprising a modified starch andpolyethylene resin.

Basically, the present invention contemplates an adhesive compositioncomprising an aqueous dispersion of modified starch and polyethyleneresin solids. The adhesive is preferably applied by means of a finelyatomized spray or other technique, such that a non-continuous film isformed on the desired substrate. That is, the adhesive should be appliedto the substrate so that it is present as discrete, non-contiguousadhesive particles.

Generally, the present invention is applicable to the rolling of anypaper stock or paper substitute, e.g., metal foils and plastic films.The invention has its greatest applicability to the rolling of consumerpaper towels, toilet tissue, industrial towels, and gift wrapping paper.However, the invention also is applicable to any type of paper stockwhich is rolled onto a core or spool; for example, business machinepaper, bag stock paper, and printing paper. The invention may also beused with the rolling of consumer plastic films such as polystyrene,cellulose acetate, and polyvinylchloride, as well as thin metals filmssuch as aluminum foil. The language "substrate material" will be usedhereafter to denote the inclusion of all of these rollable materials.However, for ease of description, the invention will usually bedescribed in terms of rolled paper products.

As previously mentioned, the adhesive composition of this invention maybe used as a transfer adhesive for bonding the first-wound sheet orportion of the substrate material to a cylindrical wrapping core whenapplied in a non-continuous film. The cylindrical core may bemanufactured from any suitable material, such as paperboard, cardboard,chip board, solid bleached sulfate, or plastic. Also, these cores may ormay not be laminated, and may or may not comprise a combination of papermaterial and plastic.

The adhesive composition of this invention is an aqueous dispersion ofpolyethylene resin and a modified starch selected from the groupconsisting of borated dextrin, gelatinized starch and pre-gelatinizedstarch. Dextrin adhesives, starch adhesives and polyethylene adhesivesare well-known in the art. Also, adhesives have been prepared bycombining dextrin and polyethylene. However, it is believed that thepresent adhesive comprising a combination of polyethylene and borateddextrin or gelatinized starch or pre-gelatinized starch is novel, andpossesses unexpectedly superior properties when utilized in the paperconverting art as a tail control or transfer adhesive. Preferably, theadhesive composition comprises from about 30-65% water by weight, fromabout 10-40% modified starch by weight, and from about 15-40%polyethylene resin emulsion by weight.

The terminology "modified starch" as used in this invention denotesgelatinized starch, pre-gelatinized starch, borated dextrin and mixturesthereof. Gelatinized starch is prepared by cooking starch in water,preferably for about 30 minutes at about 190°F. - 195°F. Starch isrelatively insoluble in cold water (tap water), but by gelatinizing thestarch it is rendered dispersible or soluble in cold water in excess of90% by weight. It has been found that the gelatinized starch for usewith this invention is preferably prepared from waxy corn starch ratherthan regular corn starch, as this provides a product with greatlyenhanced wet tack. Pre-gelatinized starch is a commercially availablestarch that has been gelatinized and then spray-dried. It can bere-dispersed by merely combining with water and agitating. Again, it ispreferred that the pre-gelatinized starch be derived from waxy cornstarch.

Dextrin is a partially hydrolyzed starch, and is an intermediate betweenstarch and sugar. Usually it is prepared by acid hydrolysis of starch inan aqueous medium. Hydrolysis is promoted by cooking, and the degree ofcooking determines the final solubility of the dextrin product.Solubility of dextrin in cold water ranges from low solubility toessentially completely soluble. It has been discovered, for purposes ofthe present invention, that the dextrin utilized should be greater than80% soluble in cold water (tap water).

Borated dextrin is prepared by reacting borax with dextrin in an aqueousmedium. Borating the dextrin increases tack of the adhesive withoutappreciably increasing total solids content thereof. The borated dextrinof the present invention may be formed in situ in the adhesiveformulation by merely adding borax to an aqueous solution of dextrin.However, it is preferred to add the borax while heating the dextrinsolution to a temperature of from about 100°F. to about 180°F. as thisresults in a superior final product. Borax, preferably Na₂ B₄ O₇ : 5H₂O, should be present in the borated dextrin in the amount of from about5-15%, basis the weight of dextrin, and preferably from about 8 to 12%,basis the weight of dextrin. The use of greater than about 15% borax mayresult in an unstable adhesive formulation, whereas the use of less thanabout 5% borax results in an adhesive formulation which does not possesssufficient tack and viscosity.

Since polyethylene resin is not soluble in water, it should beincorporated into the adhesive formulation in the form of awater/polyethylene emulsion or dispersion. These products are well-knownin the adhesive art and are available commercially from a variety ofsources. They comprise polyethylene resin solids in water, along with asuitable emulsifier. The terminology "polyethylene emulsion" will beused hereafter to refer to both dispersions and emulsions ofpolyethylene resin solids. These polyethylene emulsions generallycontain 25-60% resin solids by weight, and usually about 35-45% resinsolids. Generally, they include the lower density polyethylenes, forexample polyethylenes having molecular weights of from 10,000 to 20,000.

It has been discovered that the ratio of polyethylene solids to modifiedstarch solids in the adhesive is important and should vary according tothe type of material substrate to which the adhesive will be applied.Thus, for tail control of relatively soft paper stock (toilet tissue)the amount of polyethylene solids present in the adhesive may be as highas 40-80% basis the weight of modified starch. On the other hand, if thepaper stock is relatively coarse, the adhesive composition may containas little as 10-30% polyethylene solids based on the weight of themodified starch. For almost all rolled material substrates, andparticularly paper stock, an adhesive composition containing from about10-80% polyethylene solids basis the weight of modified starch, andpreferably from about 20- 60 % polyethylene solids basis the weight ofmodified starch solids, will be suitable. Polyethylene solids in amountsgreater than this result in the adhesive having insufficient tack, andpolyethylene solids in amounts less than this result in the adhesivehaving insufficient release characteristics. The adhesive compositionshould have a total solids content of from about 25% to 55%, andpreferably from about 35% to 50%, basis weight of the adhesivecomposition. If the solids content is too high, spraying becomesdifficult, and if solids content is too low, tack becomes a problem.

Although it is not essential, it is often desirable that the adhesiveformulation contain a minor amount, and preferably from about 0.1% to1.0% of a tack-increasing agent. Preferred tack increasing agents aresodium carbonate and sodium hydroxide. When the modified starchingredient employed is either gelatinized or pre-gelatinized starch, itis usually desirable to include a minor amount of a starch viscositystabilizer agent to prevent the starch from "setting-up" during storage.Suitable stabilizers include dicyandiamide and urea. The starchstabilizer should be present in the amount of about 5 to 10% basis theweight of starch.

Though not essential, it is often desirable to include minor amounts ofa preservative, a wetting agent, a defoaming agent, a chelating agentand/or a film-forming agent in the adhesive formulation. Theseingredients may be present in the formulation in amounts of from 0% upto about 1.0% by weight. A wide range of well-known preservatives areavailable for imparting greater stability to adhesives during storage. Awetting agent may optionally be added to the adhesive formulation tomaximize sprayability. Suitable wetting agents, such as the alkylarylpolyethers, are well-known to those in the art. Defoamers may beincorporated in order to prevent excessive foaming of the adhesiveduring mixing. A chelating agent, such as EDTA, may be added to bindmetal ions so as to improve product color. Film-forming agents such asmethyl cellulose can be added to improve film forming properties.Finally, it is sometimes desirable to include an agent which improvesadhesive penetration, for example, ethylene glycol. Such agents shouldgenerally be present in amounts of up to about 10% by weight of theadhesive.

The viscosity of the present adhesive formulation varies with therelative amounts of modified starch, polyethylene resin solids, water,and tack increasing agents present. However, the viscosity will usuallyrange from about 1 poise to about 5000 centipoise (cps). Preferably,however, the adhesive formulation will have a viscosity of from about200 to 2400 centipoise. If the viscosity is too high, spraying becomes aproblem.

We have discovered that, although the present adhesive formulation hasexcellent easy-release characteristics, release of the bound tails fromthe rolled product is also a function of the pattern of deposition ofthe adhesive on the material substrate. Thus it has been noted that evenadhesives having superior release-of-bond characteristics will causefiber tear upon separation of tails from the roll, especially when theadhesive is applied in the form of spots, globs, bands, and continuousfilms. Application of adhesive in such patterns also results in visibledepositions and staining of the paper substrate, as well as impairmentof the hand of the paper. We have discovered that application of thepresent adhesive formulation in a non-continuous film on the substrateobtains remarkably enhanced release of the tails from the rewound roll.Preferably, application of the adhesive in a non-continuous film isachieved by airless spraying of the adhesive through a nozzle. Thisobtains atomization of the adhesive so that it is deposited on the paperin small, discrete, non-continuous particles. Because of this pattern ofdeposition, there are no visible adhesive deposits on the paper andthere are no visible stains. Moreover, the paper tails remain flexible,and hand is not impaired.

Atomization can be achieved with airless spray nozzles by use of anappropriate spraying pressure. For most airless nozzles, a sprayingpressure of from about 500 to 3000 psig is sufficient to obtain desiredatomization and a non-continuous deposition of the adhesive. Preferably,the spraying pressure will vary from abut 1500 to 2500 psig, dependingon the size of the airless nozzle. Increased pressure and increasednozzle size result in increased adhesive deposition for a given unit ofspraying time. Conversely, decreased nozzle size and decreased sprayingpressure result in a smaller deposition of adhesive for a given unit ofspraying time. The deposition of a non-continuous film of adhesive canalso be achieved by application of a gravure technique, or by use of anair spray system. However, best results are obtained using an airlessspray. It also should be noted that spray systems and gravure techniquescan be utilized not only with respect to application of tail controladhesive, but also with respect to application of transfer adhesive tothe cylindrical winding cores.

The present adhesive composition is preferably applied under conditionsof ambient temperature, such as from 40° to 100°F., although it could beapplied at temperatures of up to about 130°F. Normally, the adhesivewill be applied at room temperature. Generally, the adhesive is appliedto that surface of the substrate tail (inner surface) that will contactand wrap about the rewound roll. Of course, application of the adhesivecould be made to the rewound roll itself with subsequent wrap around ofthe tail to secure same to the roll. Normally, the adhesive is appliedto the substrate tail, or roll, substantially simultaneously withcutting of the advancing substrate web and transfer thereof to a newcore. After cutting of the substrate sheet, continuing rotation of therewound roll on the rotatable mandrel causes the adhesive-carrying tailto wrap about the roll, rapidly forming a secure bond of the tail to theroll.

Application of the adhesive, when made on the rewinder, is synchronizedwith the rewinder so that any desired surface area of the tail can bedeposited with a non-continuous film of adhesive. We have found itpreferable to apply the non-continuous film across the whole width ofthe substrate tail and for several inches in length along the tail. Forexample, the non-continuous film may be applied to the inner surface ofone tail sheet when paper towels are being rewound. The amount ofadhesive applied is not critical, but should be less than that amountwhich causes visible depositions and stains. The optimum amount ofadhesive to be applied for any given substrate material is bestdetermined by trial and error. Generally, however, a very coarsesubstrate will require more adhesive than a substrate such as toiletpaper.

The adhesive composition, upon application to the substrate, isinitially very tacky and forms a secure bond between the tail and therewound roll. However, after drying through evaporation of moisture,there exists a very weak bond comprised of polyethylene resin solids andmodified starch solids. Therefore, the consumer can readily unwind thetail from the roll without tearing of the substrate material.

The following examples are presented to illustrate the invention. Itwill be understood that those examples are illustrative only, and shouldnot be considered as limiting the invention in any respect.

EXAMPLE I

The following ingredients were thoroughly blended while heating to130°F.:

                      % by weight                                                 ______________________________________                                        Water               36.15%                                                    95% soluble         26.75%                                                    dextrin                                                                       Borax               3.00%                                                     40% solids          30%                                                       polyethylene                                                                  resin emulsion                                                                14.5% caustic soda  3.35%                                                     solution                                                                      defoamer            0.15%                                                     preservative        0.10%                                                     wetting agent       0.50%                                                     ______________________________________                                    

The resulting adhesive composition was applied to toilet tissue papertails in a non-continuous film by means of an airless spray gun. Theadhesive exhibited an extremely high initial tack, and rapidly formed atail-controlling bond. Upon drying, the adhesive bond between the tailand the roll was surprisingly releasable. Moreover, the adhesive left novisible deposit or stain upon the paper, and did not impair theflexibility or hand of the paper.

EXAMPLE II

The following ingredients were thoroughly blended while heating to130°F:

                       Percentage by Weight                                       ______________________________________                                        Water                42.75%                                                   95% Soluble Dextrin  31.50%                                                   Borax                3.55%                                                    40% Solids Polyethylene                                                       Resin Emulsion       17.50%                                                   14.5% Caustic Soda                                                            Solution             3.95%                                                    Defoamer             0.15%                                                    Preservative         0.10%                                                    Wetting Agent        0.50%                                                    ______________________________________                                    

The resulting adhesive composition was applied to paper towel tails in anon-continuous film by means of an airless spray system. The adhesiveexhibited an extremely high initial tack, and immediately formed atail-controlling bond. Upon drying, the adhesive bond between the tailand the roll was easily releasable. Moreover the adhesive left novisible deposit or stain upon the paper, and did not impair theflexibility or hand of the paper towel.

EXAMPLE III

The following ingredients were thoroughly blended while heating to190°-195°F.:

                       Percentage by Weight                                       ______________________________________                                        Water                39.25%                                                   Waxy Corn Starch     26.00%                                                   40% Solids Polyethylene                                                       Resin Emulsion       31.50%                                                   Sodium Carbonate     .50%                                                     Wetting Agent        0.50%                                                    Dicyandiamide (Starch                                                         Viscosity Stabilizer)                                                                              2.00%                                                    Chelating Agent      .05%                                                     Preservative         .10%                                                     Defoamer             .10%                                                     ______________________________________                                    

The waxy corn starch gelatinized in the water during heating at190°-195°F. The resulting adhesive composition was applied to papertowel tails in a non-continuous film by means of an airless spraysystem. The concurrence of beneficial characteristics and resultsobserved with the adhesives of Examples I and II were also exhibited bythis adhesive composition.

EXAMPLE IV

The following ingredients were thoroughly blended while heating to190°-195°F.:

                       Percentage by Weight                                       ______________________________________                                        Water                61.45%                                                   Waxy Corn Starch     10.40%                                                   40% Solids Polyethylene                                                       Resin Emulsion       19.25%                                                   Ethylene glycol      6.65%                                                    Methyl cellulose     .80%                                                     Dicyandiamide (Starch                                                         Viscosity Stabilizer)                                                                              .80%                                                     Sodium Carbonate     .20%                                                     Wetting Agent        .20%                                                     Chelating Agent      .05%                                                     Defoamer             .10%                                                     Preservative         .10%                                                     ______________________________________                                    

The resulting adhesive composition was applied to toilet tissue papertails in a non-continuous film by means of an airless spray system. Thisadhesive also exhibited the same beneficial properties and resultsobserved with the adhesive compositions shown in I-I--I--III.

It will of course be understood that the optimum adhesive compositionwill vary within the foregoing guide-lines depending upon speed of therewinding system and upon the type of paper substrate or core materialto which the adhesive is being applied. Thus, for a particular substratematerial and rewinding system, the optimum properties of initial tack,releasability and sprayability will be obtained through trial and errorby adjusting the amounts and types of ingredients in the adhesive inaccordance with the foregoing guidelines.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore, only such limitations should be imposed asare indicated in the appended claims.

We claim:
 1. An improved adhesive composition comprising from about30-65% water by weight, from about 10-40% by weight of a modified starchselected from the group consisting of borated dextrin, gelatinizedstarch, pre-gelatinized starch and mixtures thereof, and from about15-40% polyethylene resin solids emulsion by weight said resin solidsbeing present in the amount of from about 10 to 80% basis the weight ofmodified starch, the total solids content of said adhesive compositionbeing from about 25% to 55% by weight.
 2. The composition of claim 1wherein the modified starch is borated dextrin containing from about5-15% borax basis the weight of dextrin and prepared from dextrin havinga solubility in cold water of greater than 80% by weight.
 3. Thecomposition of claim 1 wherein the modified starch is gelatinized starchprepared from waxy corn.
 4. The composition of claim 3 wherein a starchviscosity stabilizer is present in the adhesive in the amount of fromabout 5 to 10% basis the weight of starch.
 5. The composition of claim 4wherein the polyethylene resin solids are present in the adhesive in theamount of from about 20-60% basis the weight of starch.
 6. Thecomposition of claim 5 wherein the adhesive contains from about 35-50%total solids by weight.